The present invention relates generally to flexible exhaust pipes. More particularly, the present invention relates to flexible pipes for use in vehicular exhaust systems.
Strip wound flex pipe, also known as flex hose or flex tube, has been in existence for over 100 years. Some common uses for strip wound flex pipe include flexible electrical conduit, flexible pneumatic pipe and flexible pipe for use in truck exhaust systems.
Typically, flexible pipe is made of a strip of metal having a generally xe2x80x9cSxe2x80x9d shaped cross section including a first hook portion positioned opposite from a second hook portion. To form a pipe body, the strip of metal is wrapped in a helical pattern. As the strip of metal is wrapped in the helical pattern, the first and second hook portions of adjacent helical wraps are interlocked to form pivotal interlock seams of the pipe body. Typical metals used in manufacturing flexible pipe include galvanized steel, aluminized steel, and stainless steel.
A flexible pipe segment used in a truck exhaust system is subjected to a very harsh, destructive environment. Hence, flexible pipes in truck exhaust systems are more likely to fail sooner than flexible pipes used in less harsh environments such as electrical or pneumatic applications. Common causes of flexible pipe failure in truck exhaust systems include: (1) heat; (2) vibration; (3) displacement from frame twist and engine motor mount flexing; (4) corrosion and carbon contamination; and (5) wear.
Engine heat causes thermal expansion of the flexible pipe incorporated within an exhaust system. A new piece of flexible pipe has sufficient flexibility to inhibit thermal stresses on the exhaust system parts. Unfortunately, heat causes the flexible pipe to grow progressively more rigid with age. Consequently, older flexible pipe is subject to breakage due to thermal expansion/contraction.
Vibrations causing damage to flexible pipes in vehicle exhaust systems are commonly caused by engine vibrations and pressure pulsations in the exhaust gas flow. Such vehicular vibrations cause slight relative movement between the individual wraps of the flexible pipe. The relative movement between adjacent convolutions of the pipe causes the convolutions to rub against one another and abrade the flexible pipe.
Displacement of exhaust system piping is produced primarily when a vehicle is shifting gears, or when the vehicle frame is twisted by impacts to the frame such as road bumps. Twisting of the vehicle frame produces bending moments on the exhaust system piping and muffler that can cause breakage. Changes in torque associated with shifting gears can also cause vehicle engines to displace in their mounts thereby causing exhaust piping connected to the engines to be displaced. New flexible piping can readily absorb the movement associated with frame twist or engine torque motion. However, such movement can cause breakage of older, less flexible pipes.
Corrosion and carbon contamination also are responsible for flexible pipe failure. Depending on the choice of metal, exterior corrosion of a piece of flexible pipe is typically caused by rain, snow, and road salt. As the outside of the flexible pipe corrodes, the individual convolutions or wrapped segments become rigid with respect to one another. Heat can also cause corrosion or scaling of the metal. Carbon produced by diesel engines, along with the products of combustion such as weak acid, can further cause internal deterioration and inflexibility of flexible piping.
It The various factors mentioned above all contribute to flexible pipe failure. Typically, wear failure is caused by a combination of the above factors. For example, often a segment of flexible pipe becomes inflexible forcing all motion to be concentrated on one convolution of the flexible pipe segment. Frequently, the one convolution is located in the center of the segment. This, in turn, causes excessive motion and forces on the center of the segment which cause the flexible pipe to break at the center. Alternatively, a bending moment can be greatest at an end of a piece of flexible pipe causing the tubing to break adjacent to the clamp.
One aspect of the present invention relates to a flexible pipe adapted to be used in a vehicular exhaust system. The flexible pipe includes a pipe body that extends longitudinally along a central axis. The pipe body is made from a strip that is helically wrapped in a plurality of convolutions. The strip includes inner and outer hook portions that interlock to form an interlock seam between adjacent convolutions. The pipe body includes a flexible mid-portion positioned between first and second end portions. At least the first end portion has an axial length L1 that traverses at least several of the convolutions of the pipe body. Along the axial length L1, the first end portion defines an outer diameter D1. The mid-portion of the pipe body has an outer diameter D2. The first end portion is crushed radially inward relative to the mid-portion such that the outer diameter D1 is smaller than the outer diameter D2. The flexible pipe further includes a first transition region positioned between the first end portion and the mid-portion. The first transition region provides a diameter transition between the outer diameter D1 of the first end portion and the outer diameter D2 of the mid-portion. The first transition region has an axial length L2 that traverses at least one of the convolutions of the pipe.
The present invention provides numerous advantages. For example, the crushed first end inhibits circumferential slippage and leakage at the first end portion. Also, because the first end portion is crushed, the flexible pipe can be connected to an exhaust system by a variety of techniques such as welding, wide band clamps or narrow band clamps. Furthermore, also because the first end portion of the flexible pipe is crushed, conventional spot welds or tack welds that are typically placed at the end of a flexible pipe when the pipe is cut off can be eliminated. Moreover, because the crushed first end portion resists circumferential slippage, either standard open ended slots or captured slots can readily be used at the first end portion.
The transition region between the first end portion and the mid-portion also provides significant advantages. For example, when the flexible pipe is connected to a non-flexible pipe (e.g., a conventional solid-walled pipe), the non-flexible pipe is inserted within the flexible pipe to form a lap joint. Preferably, the non-flexible pipe is inserted within the flexible pipe such that an end of the non-flexible pipe terminates at the transition region. A clamp is then typically placed over the lap joint. During use of the exhaust system, the transition region distributes the flexible motion of the flexible pipe that would otherwise occur directly adjacent to the clamp. In this manner, the transition region assists in lengthening the useful life of the flexible pipe by inhibiting premature failure at the location immediately adjacent to the clamp. The transition region also facilitates forming a lap joint by providing additional clearance for inserting the non-flexible pipe within the flexible pipe. While the transition region provides clearance for facilitating forming the lap joint, the crushed end portion insures that an effective seal is formed at the lap joint.
A variety of additional advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.